As air travel has increased over the past decades, airport facilities have become more crowded and congested. Minimizing the time between the arrival of an aircraft and its departure to maintain an airline's flight schedule, and also to make a gate or parking location available without delay to an incoming aircraft, has become an airline priority. The safe and efficient ground movement of a large number of aircraft simultaneously into and out of the ramp and gate areas has become increasingly important. As airline fuel costs and safety concerns and regulations have increased, use of the aircraft main engines is no longer the best option for achieving the desired safe and efficient ground movement.
Various alternatives to the use of an aircraft's main engines to move an aircraft on the ground have been tried. The use of a tug or tow vehicle to move an aircraft into and out of a gate or parking location can eliminate the need to use the aircraft main engines. This option, however, is not without its own challenges and costs. More ground vehicles, requiring more fuel and more ground personnel to operate them, add to an already congested environment in the gate area. Restricted use of the aircraft engines on low power during arrival at or departure from a gate is an additional option. This option is also problematic, however. Not only does engine use consume fuel, it is also noisy, and the associated safety hazards of jet blast and engine ingestion in a congested area are significant concerns that cannot be overlooked.
The use of a motor structure integrally mounted with a wheel to rotate the wheel and drive a vehicle, including an aircraft, has been proposed. The use of such a structure, ideally, could move an aircraft with minimal or no use of an aircraft's main engines. In U.S. Pat. No. 2,430,163, for example, Dever describes a motor that may be incorporated in an aircraft landing gear wheel in which the stator is mounted on a stationary part of a wheel assembly and the rotor is connected to the revolving part of the wheel to produce a high rotating torque near the periphery of the wheel. Dever does not suggest integrating a gear assembly with this wheel structure, however. U.S. Pat. No. 3,977,631 to Jenny also describes a motor assembly selectively coupled to an aircraft wheel through a rotatably mounted brake apparatus in which the normally non-rotating stator is rotatably mounted and driven. A reduction gear assembly is included in this arrangement and is positioned to facilitate mounting of a drive motor away from the cramped wheel and brake assembly. U.S. Pat. No. 7,445,178 to McCoskey et al and U.S. Pat. No. 7,226,018 to Sullivan describe, respectively, a powered nose aircraft wheel system with a multifunctional wheel motor driven by a planetary gear assembly or a direct drive and an aircraft wheel hub motor/generator with a stack of alternating rotor and stator disks, in which the rotors are coupled to the wheel. The stator winding described by Sullivan is rigidly fixed to the axle and partially contained by a rotor, which rotates on bearings about the axle.
Electric wheel motors have been proposed for drive wheels in vehicle applications other than aircraft, particularly in electric and hybrid automobiles, in motorcycles, and in rail vehicles. In-wheel permanent magnet brushless motors with rotor elements located outwardly of stator elements with magnetic gears have been described by K. T. Chau et al in several IEEE publications. Mitsubishi Motors has proposed an outer rotor motor that does not require differential gearing for its in-wheel motor electric vehicle. In International Patent Publication No. WO2010/136868, Amutham describes a gearless wheel motor with an outer rotor that employs an arrangement of magnets mounted on both the interior stator and the exterior rotor that are selectively energized to cause the rotor to rotate about the stator in a desired clockwise or counterclockwise direction. Pfannschmidt, in U.S. Pat. No. 5,509,492, suggests a wheel hub direct drive motor with an external rotor rotatably mounted on a running gear or truck link that does not require a transmission. The use of more conventional gearing elements that can produce more output power, torque, and speed than is possible with a motor alone is not suggested by any of the foregoing disclosures. Consequently, none of these outer rotor in-wheel motor designs is structured to accommodate such gear elements.
A wheel assembly with an integral electric wheel motor concentric with a non-rotating spindle attached to a heavy vehicle with a rotor that can be positioned to rotate interiorly or exteriorly of a stator connected to a planetary gear system is described in U.S. Pat. No. 7,932,652 by DeVeny et al. Brake system components are contained within and attached to the rotor. The gear system, wheel drive, and a braking system are stated to be at least partially disposed within a predetermined axial distance defined by the stator and the rotor. The entire assembly extends well beyond the described axial distance, however, with the gear box and gearing elements located off to one side of the rotor and stator. The braking system components are located within and attached to the rotor. There is no suggestion, moreover, that the arrangement of the components of the wheel drive described by DeVeny et al could be varied.
None of the foregoing art suggests an in-wheel drive system capable of powering an aircraft drive wheel that is configured to fit within the limited space available in an aircraft landing gear wheel that integrates a gear assembly within a compact, outer rotor motor. This art, moreover, does not contemplate a compact in-wheel drive system with an integral configuration of motor and gear components that can be installed or retrofitted in existing aircraft without the modification of other landing gear structures.
U.S. Pat. No. 7,469,858 to Edelson, owned in common with the present invention, describes a gear system for an aircraft wheel motor that provides the necessary torque with reasonable system mass and a mechanism for automatically decoupling the high gear ratio needed to drive the load from the load if the load overhauls. While the aforementioned gearing system is described to be located in or near a drive wheel and preferably employs an outer rotor motor, it is not suggested that the gearing could be configured to be operationally located completely within the a wheel space with an axial dimension that is not greater than the width of the wheel tire or that is defined by the interior wheel structures.
A need exists, therefore, for a motor and gearing system that can be operationally integrated within a minimal space in an aircraft or other vehicle wheel to generate optimum torque for driving the wheel on the ground. A need further exists for a compact gearing system for a vehicle, including an aircraft, drive wheel specifically configured to drive a correspondingly compact motor with an outer rotor element and an inner stator element mounted completely within the volume defined by the interior of the wheel and an axial dimension represented by the width of a tire mounted on the wheel.